MSHA Reduces Asbestos PEL by 95 Percent

An MSHA final rule published today lowers the limit for an eight-hour, time-weighted average full-shift PEL from 2 asbestos fibers per cubic centimeter of air (f/cc) to 0.1 f/cc at all metal and nonmetal mines, surface coal mines, and surface areas of underground coal mines. The existing excursion limit for metal and nonmetal mines, 10 fibers per milliliter (f/mL) for 15 minutes, and the existing excursion limit for coal mines, 10 f/cc for a total of one hour in each eight-hour day, are both being cut to 1 f/cc for 30 minutes. The final rule takes effect April 29. These new PELS are the same as in MSHA's proposed rulemaking in July 2005 and also the same as OSHA's current asbestos exposure limits.

Today's rule notes that OSHA stated in the preamble to its 1994 final rule that there is a remaining significant risk of material impairment of health or functional capacity at the 0.1 f/cc limit, but that concentration is "the practical lower limit of feasibility for measuring asbestos levels reliably." MSHA said today it agrees with this conclusion. MSHA said it will continue to use phase contrast microscopy (PCM) as its primary methodology for analyzing air samples to determine compliance with the PELs and will continue to follow up with a transmission electron microscopy (TEM) analysis when PCM results indicate a potential overexposure, but it wants to encourages the development of analytical methods specifically for asbestos in mine air samples.

MSHA's and OSHA's regulations address the same six asbestos minerals: chrysotile, crocidolite, cummingtonite-grunerite asbestos (amosite), actinolite asbestos, anthophyllite asbestos, and tremolite asbestos. The rule illustrates how the agencies' asbestos PELs have dropped, with MSHA's 30 f/mL limit in 1967 falling to 12 f/mL in 1969, 5 f/mL in 1974 for metal and nonmetal mines, 2 f/cc in 1976 for surface areas of coal mines, and 2 f/mL in 1978 for metal and nonmetal mines. OSHA's PEL went from 12 f/cc in 1971 to 5 f/cc the same year, 2 f/cc in 1972, 0.5 f/cc in 1983, 0.2 f/cc in 1986, and 0.1 f/cc in 1994.

MSHA's air sampling at 207 mines from Jan. 1, 2000 through May 31, 2007, found 29 mines with at least one miner exposed to a TWA fiber concentration exceeding 0.1 f/cc, and 113 of 917 personal full-shift fiber results exceeded 0.1 f/cc using the existing PCM-based analytical screening method. Further analysis of the 113 samples with TEM confirmed asbestos fiber exposures exceeded 0.1 f/cc in 23 of them. "Although MSHA has no evidence of asbestos exposure above the new PEL in coal mines, the Agency anticipates that some coal mines will encounter asbestos from asbestos containing materials brought onto mine property. These operators may have to take corrective action," the agency said in today's rule.

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    September 2021

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